OSTEODESMACEA. MOLLUSCA. COCHLODESMA. 49 



COCHLODLSMA LEA'NA. 



Shell thin, white, sub-oval, the shorter side of the right or 

 more convex valve truncated ; rib-like support directed backwards. 



FIGURES 29, 30. 

 State Coll., No. 230. Soc. Cab., No. 1726. 



Anatlna Leana, CONRAD ; Journ. Acad. JVat. Sc., vi. 263, pi. 11, f. 11. 

 Cochlodesma Leana, CODTHOUY ; Bost. Journ. Nat. Hist., ii. 170. 



Shell sub-oval, thin and brittle, white, with a thin, yellowish 

 epidermis ; the right valve convex, and truncated at the shorter 

 end ; the left valve nearly flat, and rounded at both ends ; posterior 

 end gaping, a little the shortest, and usually a little the narrowest ; 

 beaks very small, scarcely prominent, cleft at one side ; a faint, 

 wave-like ridge passes from them to the lower posterior angle ; 

 surface slightly wrinkled by the lines of growth, somewhat pearly 

 beneath ; interior chalky-white, the muscular and palleal impres- 

 sions superficial, pearly. The spoon-shaped hinge process nearly 

 horizontal, directed across the shell, and resting on a rib-like sup- 

 port, directed to the posterior muscular impression, immediately 

 in front of which is another thread-like branch in the direction of 

 the cleft in the beak. Ossiculum none. Length 1| inch, 

 height 1 inch nearly, breadth / inch. 



Found about Cape Cod in almost every direction, inhabiting 

 sandy beaches ; also about Nantucket. I have never heard of it 

 on the north shore of Massachusetts Bay, but it is more abun- 

 dant to the south of us. 



The animal has the mantle closed in front, except an opening for a 

 broad, compressed foot, extending the whole length of the small ab- 

 dominal mass ; edges of the mantle a little thickened and wrinkled ; 

 siphons long, slender, separate in their whole extent. 



This genus, proposed by Mr. Couthouy, has, I observe, been ad- 

 mitted by J. E. Gray, in the " Annals of Science," and I have there- 

 fore adopted it without hesitation. 



This species very closely resembles Mya (Cochlodesma) pratenuis 

 of Pennant (Ligula pratenuis, Montagu), but differs in being more 

 rounded, less convex, less narrowed behind, and has no signs of a 

 granulated or shagreened epidermis, like that shell. 



7 



